Mercury removal method and system

ABSTRACT

The present invention provides a mercury removal method which can effectively remove very small amounts of mercury components present in a gas during wet gas purification such as coal or heavy oil gasification gas purification and petroleum refining. A mercury removal method for the removal of mercury present in a gas, the method comprising the steps of bringing a gas containing at least mercury and not less than 10 ppm of hydrogen sulfide into gas-liquid contact with an absorbing fluid under pressurized conditions so as to cause mercury to pass into the absorbing fluid; flashing the mercury-containing absorbing fluid under lower-pressure conditions to separate it into gaseous components and liquid components; and removing the mercury contained in the separated gaseous components by adsorption to an adsorbent.

FIELD OF THE INVENTION

[0001] This invention relates to a mercury removal method and system foruse in wet gas purification. More particularly, it relates to a mercuryremoval method which can effectively remove very small amounts ofmercury components present in a gas during wet gas purification such ascoal or heavy oil gasification gas purification and petroleum refining.

BACKGROUND OF THE INVENTION

[0002] Exhaust gas from coal-fired thermal electric power plantscontains mercury originating from coal. This mercury cannot becompletely removed in a conventional flue gas treatment system(including an electrostatic precipitator, a wet flue gas desulfurizerand the like), and some of it is discharged therefrom. Since mercury isa trace component and has a very high vapor pressure and, in particular,metallic mercury has the property of being insoluble in water, it isdifficult to remove mercury by recovering it with a dust collector or bywashing the gas with a scrubber.

[0003] A large amount of mercury is discharged from conventional wastedisposal by incineration or the like, but the scale of disposal isrelatively small and produces a small volume of gas. Accordingly, suchmercury has frequently been treated, for example, by adsorption usingactivated carbon. While treating methods involving adsorption byactivated carbon are effective methods for the removal of such mercury,they are not suitable for practical use in the treatment of a largevolume of gas because an enormous consumption cost is required.

[0004] Consequently, a mercury removal method has been proposed in whichan oxidizing agent is sprayed, for example, in a mist eliminator (M/E)installed downstream of a flue gas desulfurizer. Since it is difficultto use activated carbon in thermal electric power plants for theabove-described reason, this method provides a more convenient means forremoving mercury by spraying an oxidizing agent in a mist eliminator.

[0005] Moreover, a process has been proposed in which metallic Hg isoxidized to HgCl₂ on a catalyst such as a denitration catalyst and thisHgCl₂ is removed in a flue gas desulfurizer.

[0006] Mercury exists chiefly in two forms: metallic mercury (Hg) ofzero valence and mercury chloride (HgCl₂). While metallic mercury ishardly soluble in water, mercury chloride is relatively soluble inwater. Thus, mercury in the form of mercury chloride can be removed bymeans of a desulfurizer. Accordingly, metallic mercury of zero valencecan be removed by oxidizing it to mercury chloride with the aid of anoxidizing agent.

[0007] In this process, therefore, a chlorinating agent such as Cl₂ orHCl is added and sprayed just before a denitration catalyst within adenitrator, so that metallic mercury is oxidized on the denitrationcatalyst.

[0008] In ordinary exhaust gases, all mercury is not present in the formof metallic mercury. A certain proportion thereof is present in the formof mercury chloride because coal has a high chlorine content, and thismercury component can be removed. Accordingly, a chlorinating agent maybe used for the remaining metallic mercury.

[0009] However, examination of the mercury contained, for example, incoal or heavy oil gasification gas has revealed that almost all mercuryis present as metallic mercury under a reducing atmosphere and little isdissolved in water. Accordingly, if an oxidizing agent is sprayed underan atmosphere of a reducing gas during wet gas purification, theoxidizing agent will be wasted owing to the presence of various reducingsubstances and cannot be expected to produce any beneficial effect.

[0010] Moreover, if a chlorinating agent is continuously sprayed toinduce a reaction on the catalyst, a gasification gas having a highammonia content and a high pressure undergoes the reaction of ammoniawith HCl resulting in the precipitation of ammonium chloride (NH₄Cl).This ammonium chloride may cause a problem in that it is likely toaccumulate in such units as GGHs and block them up.

SUMMARY OF THE INVENTION

[0011] In view of the above-described problems, the present inventorsmade intensive investigations in order to develop a mercury removalmethod which can remove mercury, as a trace component in gases,effectively and efficiently, which can reduce the mercury removal costresulting from the operation of the system, and which requires asimplified procedure and system and can hence be carried out easily.

[0012] As a result, the present inventors have now found that thecoexistence of H₂S in a gasification gas causes metallic mercury to passinto water and that the so-collected is released into the gaseous phasewhen the water is exposed to a lower pressure (or flashed). That is, inthe case of wet gas purification, the coexistence of hydrogen sulfide inthe water washing step permits Hg to pass into the absorbing fluid andbe removed thereby, and the Hg captured in the water washing step can bereleased into the gaseous phase by returning the Hg-containing wastewater from the elevated pressure to atmospheric pressure. Thus, it hasalso been found that the above-described problems can be solved byremoving mercury according to a method utilizing such phenomena. Thepresent invention has been completed from this point of view.

[0013] Specifically, the present invention provides a mercury removalmethod for the removal of mercury components present in a gas during wetgas purification, the method comprising a water washing step forbringing a gas containing mercury components into contact with anabsorbing fluid under pressurized conditions including the presence ofnot less than 10 ppm and preferably not less than 100 ppm of hydrogensulfide so as to cause mercury components to pass from the gas into theabsorbing fluid; a flashing step subsequent to the water washing step,for spraying the discharged absorbing fluid under a lower pressure toseparate it into gaseous components and waste water; and an adsorptionremoval step for passing the gaseous components through a mercuryremover provided with an adsorbent to remove mercury componentstherefrom by adsorption. In this mercury removal method, it ispreferable to dissolve mercury components in the absorbing fluid, forexample, under an elevated pressure of 0.2 to 5.0 MPa and in thecoexistence of about 500 ppm to 10% of hydrogen sulfide, and remove theflashed mercury components by adsorption to activated carbon used as theadsorbent. Preferably, the activated carbon has an S component depositedthereon.

[0014] The present invention also provides a mercury removal system forthe removal of mercury present in a gas during wet gas purification, thesystem comprising a water washing tower in which a gas containing bothmercury components and hydrogen sulfide is introduced thereinto and anabsorbing tower is circulated through the tower under pressurizedconditions so as to cause mercury components to pass into the absorbingfluid; a flash drum in which the absorbing fluid discharged from thewater washing tower is sprayed under a lower pressure to separate itinto gaseous components and waste water; and a mercury remover providedwith an adsorbent in which the mercury components present in the gaseouscomponents are removed by adsorption. Typically, the aforesaid waterwashing tower comprises a gas cooling tower and a gas cleaning tower. Inthis system having a flash drum and a mercury remover installed on thedownstream side of the water washing tower, about 50 to 95% of themercury present in the formed gas introduced into the system can beremoved.

[0015] The present invention also provides the above-described systemthat further comprises a hydrogen sulfide absorption tower in which thewater-washed gas fed from the aforesaid water washing tower introducedthereinto and an absorbing fluid containing an amine compound is used toremove hydrogen sulfide by absorption into the absorbing fluid; a secondflash drum in which the absorbing fluid discharged from the hydrogensulfide absorption tower is sprayed under a lower pressure to separateit into gaseous components and an absorbing fluid to be fed to aregeneration tower; and a mercury remover provided with an adsorbent inwhich the mercury components present in the gaseous components deliveredfrom the second flash drum are removed by adsorption. In this systemhaving a flash drum and a mercury remover installed on the downstreamside of the hydrogen sulfide absorption tower, about 50 to 95% of themercury present in the water-washed gas introduced into the hydrogensulfide absorption tower can be removed.

[0016] In the present invention, Hg can be removed by the coexistence ofhydrogen sulfide in the water washing tower of the system. That is, ifthe gas being treated is a system involving the coexistence of hydrogensulfide, Hg passes into the water present in the water washing tower andcan hence be removed from the gas. As a result, Hg is contained in wastewater discharged from the water washing tower.

[0017] When the collected Hg-containing waste water is returned from theelevated pressure to atmospheric pressure, Hg is released into thegaseous phase. Specifically, Hg is dispersed into the gaseous phase bypassing the waste water through a flash drum.

[0018] Since hydrogen sulfide is usually present in a gasification gassubjected to gas purification, Hg present in the gas passes into anabsorbing fluid within a water washing tower. After this absorbing fluidis passed through a flash drum to recover gaseous components, Hg can beadsorbed and captured by passing the gaseous components through anadsorbent. The present invention comprises a system in whichHg-containing gaseous components separated by flashing is passed throughan adsorbent to remove mercury therefrom by means of the adsorbent.Thus, as compared with the case in which the whole gasification gas isdirectly treated with an adsorbent prior to its introduction into thesystem, Hg can be removed by treating a much smaller volume of gas, andthe operating cost required for treatment with an adsorbent can bemarkedly reduced.

[0019] Thus, the present invention makes it possible to remove mercury,as a trace component in gases, effectively and efficiently and also toreduce the mercury removal cost resulting from the operation of thesystem.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a diagram illustrating an outline of a system suitablefor carrying out the wet gas purification process of the presentinvention.

[0021]FIG. 2 is a diagram schematically showing the construction of thepurification system used in Example 1.

[0022]FIG. 3 is a diagram schematically showing the construction of thepurification system used in Example 2.

[0023]FIG. 4 is a diagram schematically showing the construction of thepurification system used in Example 3.

[0024] The reference numerals shown in these figures are defined asfollows: 1 Gas cooling tower; 2 Gas cleaning tower; 3 Flash drum; 4Mercury remover; 5 Hydrogen sulfide absorption tower; 6 Absorption fluidregeneration tower; 7 Circulating pump; 8 Flash drum; 9 Absorbing fluidheat exchanger; 10 Gasification furnace; 11 Cyclone; 12 Filter; 13 COSconverter; 14 Gas-gas heat exchanger; 15 Mercury remover; 20,21 Flashdrum.

DETAILED DESCRIPTION OF THE INVENTION

[0025] A specific embodiment of the wet gas purification process inaccordance with the present invention will be described hereinbelow withreference to the accompanying drawings.

[0026]FIG. 1 schematically illustrates an exemplary system in accordancewith this embodiment which is suitable for carrying out the mercuryremoval method of the present invention during wet gas purification. Inthe system of this embodiment, the water washing step comprises acooling step and a cleaning step. The cooling step is carried out in agas cooling tower 1, and the cleaning step is carried out in a gascleaning tower 2. Water used to absorb the ammonia component present inthe gas is introduced, for example, into gas cleaning tower 2. These twowater washing towers serve to remove ammonia present in the gas byabsorption into an absorbing fluid. The water introduced into gascleaning tower 2 is circulated by means of a pump 7 and acts as anabsorbing fluid for absorbing ammonia. A portion thereof is fed to gascooling tower 1 installed on the upstream side with respect to thedirection of gas flow, and is also circulated through the tower by meansof a pump 7. The present invention may also be practiced in anembodiment in which the cooling and cleaning steps are carried out in asingle water washing tower. Alternatively, sulfuric acid may be added tothe absorbing fluid within gas cooling tower 1.

[0027] In the above-described water washing step for the removal ofammonia, when mercury components are contained in the introduced gas andnot less than 10 ppm of hydrogen sulfide is also contained therein, themercury components pass into the absorbing fluid under pressurizedconditions in the water washing towers (i.e., the cooling tower and thecleaning tower). Since the passage of mercury components into theabsorbing fluid is influenced by temperature, the degree of mercuryremoval from the gas is enhanced as the temperature of the fluid becomeslower. Accordingly, it is believed that the degree of mercury removal isinfluenced by the temperatures of gas cooling tower 1 and gas cleaningtower 2, and the degree of mercury removal is enhanced as thetemperature of gas cleaning tower 2 installed on the downstream sidebecomes lower. From the viewpoint of mercury removal, it is preferableto operate gas cleaning tower 2 usually at 50° C. or below andpreferably at 40° C. or below.

[0028] Next, the mercury-containing absorbing fluid discharged from theabove-described water washing step is transferred to a flashing stepusing a flash drum 3, in which it is sprayed under a lower pressure.Thus, the absorbing fluid is separated into gaseous components and wastewater.

[0029] In such purification treatment systems, the waste waterdischarged from the water washing step generally has a high pressure andhence contains various gases dissolved therein. In order to treat suchwaste water, it is common practice to depressurize the waste water inflash drum 3 and thereby release it from the elevated pressure. Thus,the gases dissolved therein are once flashed and released into thegaseous phase. Then, the remaining solution is subjected to a wastewater treatment.

[0030] Where an ordinary formed gas is treated, the flashed gascomponents are burned in a combustion furnace or discharged into theatmosphere. However, where the gas being treated according to thepresent invention is a mercury-containing gas, these gas componentsinclude mercury. The reason for this is believed that, when theabsorbing fluid into which mercury has passed in the water washing stepis sprayed under a lower pressure, the mercury, together with othergases, is suspended or dispersed in the gaseous phase.

[0031] Accordingly, the gaseous components separated in the aforesaidflash drum 3 are passed through a mercury remover 4 provided with anadsorbent (e.g., activated carbon). In this mercury remover 4, mercurycomponents present in the gas are removed by adsorption to activatedcarbon used as the adsorbent. The exhaust gas from which mercury hasbeen removed by passage through mercury remover 4 is then fed to anoff-gas combustion furnace.

[0032] On the other hand, the mercury removal system of this embodimentas illustrated in FIG. 1 also serves to remove mercury components fromthe water-washed gas transferred from the aforesaid water washing towersto a hydrogen sulfide absorption tower.

[0033] In the above-described water washing step for the removal ofammonia, a certain proportion of mercury components pass from themercury-containing gas into the absorbing fluid. However, some mercurycomponents still remain in the water-washed gas and transferred to afurther stage of the wet gas purification system. On the downstream sideof the water washing step, there is provided a hydrogen sulfide removalstep for removing hydrogen sulfide present in the gas. In this step,mercury components present in the gas are also removed. The hydrogensulfide removal step includes an H₂S absorption tower 5 and an absorbingfluid regeneration tower 6. The water-washed gas transferred from thewater washing step is introduced into hydrogen sulfide absorption tower5.

[0034] The main purpose of hydrogen sulfide absorption tower 5 is toremove hydrogen sulfide by absorption into an absorbing fluid containingan amine. According to this embodiment, in this hydrogen sulfideabsorption tower 5, mercury components are allowed to pass from themercury- and hydrogen sulfide-containing gas into the absorbing fluidunder pressurized conditions (water washing step). Thus, theamine-containing absorbing fluid also contains mercury components.Accordingly, the absorbing fluid discharged from hydrogen sulfideabsorption tower 5 is introduced into a second flash drum 8, in which itis sprayed under a lower pressure and separated into gaseous componentsand an absorbing fluid to be fed to the regeneration tower.

[0035] Subsequently, in the embodiment, the gaseous components separatedin the aforesaid flash drum 8 are passed through mercury remover 4provided with activated carbon, similarly to the gaseous components fromthe aforesaid flash drum 8. In this mercury remover 4, mercurycomponents present in the gas are removed by adsorption to activatedcarbon. The exhaust gas from which mercury has been removed by passagethrough mercury remover 4 is then fed to an off-gas combustion furnace.

[0036] The gaseous components separated in flash drum 8 may betransferred to a second mercury remover installed separately frommercury remover 4 and treated by adsorption to activated carbon.

[0037] In addition to activated carbon, the adsorbent may comprise achelate resin, elemental sulfur or a sulfur compound supported on acarrier comprising at least one compound selected from the groupconsisting of Al₂O₃, TiO₂ and SiO₂, or zeolite.

[0038] While several embodiments of the present invention have beendescribed, it is to be understood that the present invention is notlimited to the above-described embodiments, but various changes andmodifications may be made without departing from the spirit and scope ofthe invention. The present invention is further illustrated by thefollowing examples. However, these examples are not to be construed tolimit the scope of the invention.

EXAMPLE 1

[0039]FIG. 2 illustrates an outline of a wet gas purification systemused in this example.

[0040] In a gasification furnace 10, coal fed thereto was converted to agasification gas, which was passed through a cyclone 11 installeddownstream thereof and then through a filter 12, and fed to a COSconverter 13. The feed rate of coal was 10 kg/h. Subsequently, theformed gas passed through a gas-gas heat exchanger 14 and thenintroduced into a wet gas purification process. The pressure of theformed gas was 0.9 MPa and the flow rate thereof was 22.4 m³N/h(d).Prior to the water washing step, the formed gas had an H₂S concentrationof 800 to 1,000 ppm and a temperature (T₁) of about 200° C.

[0041] The water washing step includes two towers: a gas cooling tower 1installed on the upstream side and a gas cleaning tower 2 installed onthe downstream side as viewed from the direction of gas flow. The gastemperature (T₂) at the outlet of gas cooling tower 1 was 80° C., theflow rate of the fluid circulated through gas cooling tower 1 was 601/h, and the flow rate of waste waster from gas cooling tower 1 was 1.91/h. Moreover, the gas temperature (T₃) at the outlet of gas cleaningtower 2 was 40° C., and the flow rate of the fluid circulated throughgas cleaning tower 2 was 100 1/h.

[0042] The mercury-containing absorbing fluid discharged from the waterwashing step was sprayed in a flash drum 20. The separated gaseouscomponents were introduced into a mercury remover 4, where mercury wasremoved from the gas. The amount of the gas flashed from waste water was30 1N/h.

[0043] On the other hand, the gas freed of ammonia in the water washingstep was fed to a hydrogen sulfide absorption tower 5. The gastemperature (T₄) at the outlet of H₂S absorption tower 5 was 40° C., andthe flow rate of the fluid circulated through H₂S absorption tower 5 was30 1/h.

[0044] With respect to the above-described system of FIG. 2, Hgconcentrations were measured at various positions S1 to S6 in thesystem. The results thus obtained are shown in Table 1 below. TABLE 1Item Hg concentration at gas cooling 0.0056 tower inlet, S1 (mg/m³N) Hgconcentration at gas cleaning 0.0014 tower outlet, S2 (mg/m³N) Hgconcentration at H₂S absorption 0.0004 tower outlet, S3 (mg/m³N) Hgconcentration in waste water 0.001 from gas cooling tower, S4 (mg/l) Hgconcentration in flashed gas 3.0 from waste water, S5 (mg/m³N) Hgconcentration at Hg adsorption <0.01 remover outlet, S6 (mg/m³N)

[0045] The difference between concentrations S1 and S2 given in Table 1(i.e., S1-S2) is the amount of mercury which was removed by the waterwashing step. Moreover, when the gaseous components separated byflashing waste water were passed through mercury remover 4, the mercuryconcentration was reduced from 3.0 mg/m³N (S5) to less than 0.01 mg/m³N(S6). It has been confirmed by these results that mercury passes intothe waste water discharged from the water washing step and mercurycomponents can be effectively removed from the gaseous componentsseparated by flashing the waste water.

EXAMPLE 2

[0046]FIG. 3 illustrates an outline of a wet gas purification systemused in this example.

[0047] In addition to the system of Example 1, this example includes anadditional step in which the mercury (Hg) removed into the absorbingfluid in hydrogen sulfide absorption tower 5 was introduced into a flashdrum 21 to release it into the gaseous phase and then removed by meansof a mercury remover 15 using activated carbon or the like. Theconditions concerning the formed gas and the flow rates and temperaturesemployed in the water washing step were the same as those described inExample 1. The amount of the gas separated by flashing the H₂S absorbinggas in flash drum 21 was 50 1N/h.

[0048] With respect to the above-described system of FIG. 3, Hgconcentrations were measured at various positions S1 to S9 in thesystem. The results thus obtained are shown in Table 2 below. TABLE 2Item Hg concentration at gas cooling 0.0056 tower inlet, S1 (mg/m³N) Hgconcentration at gas cleaning 0.0014 tower outlet, S2 (mg/m³N) Hgconcentration at H₂S absorption 0.0004 tower outlet, S3 (mg/m³N) Hgconcentration in waste water 0.001 from gas cooling tower, S4 (mg/l) Hgconcentration in flashed gas 3.0 from waste water, S5 (mg/m³N) Hgconcentration at Hg adsorption <0.01 remover outlet, S6 (mg/m³N) Hgconcentration in H₂S absorbing <0.005 fluid, S7 (mg/l) Hg concentrationin flashed gas 0.45 from H₂S absorbing fluid, S8 (mg/m³N) Hgconcentration at Hg adsorption <0.01 remover outlet, S9 (mg/m³N)

[0049] The difference between concentrations S2 and S3 given in Table 2(i.e., S2-S3) is the amount of mercury which was removed by washing withthe absorbing fluid within the hydrogen sulfide absorption tower.Moreover, when the gaseous components separated by flashing theabsorbing fluid were passed through mercury remover 15, the mercuryconcentration was reduced from 0.45 mg/m³N (S8) to less than 0.01 mg/m³N(S9). It has been confirmed by these results that, also in the hydrogensulfide absorption step subsequent to the water washing step, mercurypasses into the absorbing fluid and mercury components can beeffectively removed from the gaseous components separated by flashingthe absorbing fluid.

EXAMPLE 3

[0050]FIG. 4 illustrates an outline of a wet gas purification systemused in this example.

[0051] In addition to the system of Example 2, this example includes anadditional step in which the exhaust gas having passed through gas-gasheat exchanger 14, which was directly discharged in Example 2, waspassed through heat exchangers and then burned in a combustor. In thisexample, the feed rate of coal was 1,000 kg/h, the flow rate of theformed gas was 3,500 m³N/h, the H₂S concentration in the formed gas was800 to 1,000 ppm, the gas temperature (T₂) at the outlet of gas coolingtower 1 was 40° C., the flow rate of the fluid circulated through gascooling tower 1 was 8.4 tons/h, the flow rate of waste waster from gascooling tower 1 was 0.4 ton/h, the amount of the flashed gas producedfrom waste water in flash drum 20 was 0.2 m³N/h, the gas temperature(T₃) at the outlet of gas cleaning tower 2 was 40° C., the flow rate ofthe fluid circulated through gas cleaning tower 2 was 10 tons/h, the gastemperature (T₄) at the outlet of H₂S absorption tower 5 was 40° C., theflow rate of the fluid circulated through H₂S absorption tower 5 was 3.6tons/h, and the amount of the flashed gas produced from the H₂Sabsorbing fluid was 1.6 m³N/h. Other conditions were the same as in

EXAMPLE 2

[0052] With respect to the above-described system of FIG. 4, Hgconcentrations were measured at various positions S1 to S9 in thesystem. The results thus obtained are shown in Table 3 below. TABLE 3Item Hg concentration at gas cooling 0.005 tower inlet, S1 (mg/m³N) Hgconcentration at gas cleaning 0.0013 tower outlet, S2 (mg/m³N) Hgconcentration at H₂S absorption 0.0003 tower outlet, S3 (mg/m³N) Hgconcentration in waste water <0.005 from gas cooling tower, S4 (mg/l) Hgconcentration in flashed gas 63 from waste water, S5 (mg/m³N) Hgconcentration at Hg adsorption <0.01 remover outlet, S6 (mg/m³N) Hgconcentration in H₂S absorbing <0.005 fluid, S7 (mg/l) Hg concentrationin flashed gas 2.2 from H₂S absorbing fluid, S8 (mg/m³N) Hgconcentration at Hg adsorption <0.01 remover outlet, S9 (mg/m³N)

[0053] It has been confirmed by these results that, even when a largevolume of formed gas is subjected to wet gas purification, the mercuryremoval method of the present invention can reduce the Hg concentrationin exhaust gas to less than 0.01 mg/m³N at all of positions S6 to S9.

[0054] According to the mercury removal method of the present invention,the volume of gas being treated can be markedly decreased by treatingflashed gas, and the operating cost required for the treatment can alsobe reduced, as compared with the case in which the formed gas isdirectly treated. Moreover, since no energy supply to the mercuryremoval (or absorption) step and the Hg flashing step is required forthe purpose of mercury removal, Hg can be positively removed withoutmodifying an ordinary purification system substantially.

[0055] Furthermore, the adsorbent for the adsorption of Hg can be usedat low temperatures (400° C. or below) and only a small amount ofadsorbent is required because of its high rate of Hg removal. Inaddition, since a gas once dissolved in water is treated with activatedcarbon, hydrocarbons and other substances capable of inhibiting Hgadsorption are not present therein.

1. A mercury removal method for the removal of mercury present in a gas,said method comprising the steps of bringing a gas containing at leastnot less than 10 ppm of hydrogen sulfide and mercury into gas-liquidcontact with an absorbing fluid under pressurized conditions so as tocause mercury to pass into the absorbing fluid; flashing themercury-containing absorbing fluid under lower-pressure conditions toseparate it into gaseous components and liquid components; and removingthe mercury contained in the separated gaseous components by adsorptionto an adsorbent.
 2. A mercury removal method as claimed in claim 1 whichcomprises the steps of bringing a gas containing at least not less than10 ppm of hydrogen sulfide and mercury into gas-liquid contact with anabsorbing fluid under pressurized conditions so as to cause mercury topass into the absorbing fluid; bringing the gas freed partially ofmercury into gas-liquid contact with an absorbing fluid containing anamine compound so as to cause hydrogen sulfide and mercury present inthe gas to be absorbed into the absorbing fluid; flashing each of theabsorbing fluids under a lower pressure to separate it into amercury-containing gas and a liquid; and removing mercury from themercury-containing gases by adsorption to an adsorbent.
 3. A mercuryremoval method as claimed in claim 1 or 2 wherein the gas containing atleast not less than 10 ppm of hydrogen sulfide and mercury is coalgasification gas or heavy oil gasification gas.
 4. A mercury removalmethod as claimed in any of claims 1 to 3 wherein the adsorbent foradsorbing mercury comprises a chelate resin, elemental sulfur or asulfur compound supported on a carrier comprising at least one compoundselected from the group consisting of Al₂O₃, TiO₂ and SiO₂, activatedcarbon or zeolite.
 5. A mercury removal method for the removal ofmercury components present in a gas during wet gas purification, saidmethod comprising: a water washing step for bringing a gas containingmercury components into contact with an absorbing fluid underpressurized conditions including the presence of not less than 10 ppm ofhydrogen sulfide so as to cause mercury components to pass from the gasinto the absorbing fluid; a flashing step subsequent to the waterwashing step, for spraying the discharged absorbing fluid under a lowerpressure to separate it into gaseous components and waste water; and anadsorption removal step for passing the gaseous components through amercury remover provided with an adsorbent to remove mercury componentstherefrom by adsorption.
 6. A mercury removal method as claimed in claim5 wherein the adsorbent comprises a chelate resin, elemental sulfur or asulfur compound supported on a carrier comprising at least one compoundselected from the group consisting of Al₂O₃, TiO₂ and SiO₂, activatedcarbon or zeolite.
 7. A mercury removal system for the removal ofmercury present in a gas during wet gas purification, said systemcomprising a water washing tower in which a gas containing both mercurycomponents and hydrogen sulfide is introduced thereinto and an absorbingtower is circulated through the tower under pressurized conditions so asto cause mercury components to pass into the absorbing fluid; a flashdrum in which the absorbing fluid discharged from the water washingtower is sprayed under a lower pressure to separate it into gaseouscomponents and waste water; and a mercury remover provided with anadsorbent in which the mercury components present in the gaseouscomponents are removed by adsorption.
 8. A mercury removal system asclaimed in claim 7, said system further comprising a hydrogen sulfideabsorption tower in which the water-washed gas fed from the waterwashing tower introduced thereinto and an absorbing fluid containing anamine compound is used to remove hydrogen sulfide by absorption into theabsorbing fluid; a second flash drum in which the absorbing fluiddischarged from the hydrogen sulfide absorption tower is sprayed under alower pressure to separate it into gaseous components and an absorbingfluid to be fed to a regeneration tower; and a mercury remover providedwith an adsorbent in which the mercury components present in the gaseouscomponents delivered from the second flash drum are removed byadsorption.
 9. A mercury removal system as claimed in claim 7 or 8wherein the adsorbent comprises a chelate resin, elemental sulfur or asulfur compound supported on a carrier comprising at least one compoundselected from the group consisting of Al₂O₃, TiO₂ and SiO₂, activatedcarbon or zeolite.